Construction method, tubular member, and nuclear power plant

ABSTRACT

A construction method of a pipeline that forms a pipeline by joining tubular members to each other by butt welding, includes: a tubular member preparation step for preparing a tubular member having a smooth length of an outer surface along an axial direction from a joined end, which is set based on conditions of ultrasonic inspection of a welded portion, which are determined by usage conditions of the pipeline; a tubular member welding step for welding together prepared tubular members; and a welded portion inspection step for inspecting a welded portion by ultrasonic inspection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pipeline construction method, atubular member, and a nuclear power plant that is furnished with thetubular member.

Priority is claimed on Japanese Patent Application No. 2011-002945,filed Jan. 11, 2011, the content of which is incorporated herein byreference.

2. Description of Related Art

At nuclear power plants for power generation, inspections areperiodically performed in order to ensure the safety and the reliabilitythereof. Further, the structures, the systems, and the equipment of thenuclear power plant are classified according to the importance of theirsafety features, and the “Standards for Nuclear Power Plants:Maintenance Standards” published by the Japan Society of MechanicalEngineers is applied to maintenance control operations and the like, ofthese classified structures, systems, and equipment.

Moreover, non-destructive inspection is applied to the inspection ofpiping, pressure vessels, and the like, of the nuclear power plant, andwith regard to welded portions M where tubular members are joined toeach other by butt welding, such as with piping to piping, nozzle 2 of anuclear reactor pressure vessel 1 to piping 3, or a valve to piping, theinspection method and the inspection area are prescribed according tothe “Standards for Nuclear Power Plants: Maintenance Standards” (referto FIG. 6).

More specifically, it is prescribed that, with regard to the weldedportion M of both of the tubular members 2 and 3 of the nuclear powerplant, the inspection thereof is performed by ultrasonic inspection(refer to Patent Document 1 for example). Furthermore, in class 1 wherethe importance of safety features is high (equipment that constitutesthe nuclear reactor coolant pressure boundary (vessels, piping, pumps,valves) for example), as shown in FIG. 7A, it is prescribed that theinspection is performed with the entire plate thickness t from the innersurface 4 to the outer surface 5 of the welded portion M as the flawinspection area S. Moreover, in class 2 where the importance of thesafety features is lower than in class 1, as shown in FIG. 7B, it isprescribed that the inspection is performed with a plate thickness areaof ⅓ of the designed plate thickness t from the inner surface 4 of thewelded portion M as the flaw inspection area S.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2005-221265.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

For example, as shown in FIG. 6, FIG. 7A, and FIG. 7B, with regard tothe nozzle 2 provided on the nuclear reactor pressure vessel 1, and thepiping 3 that forms a pipeline R by butt welding to this nozzle 2 (boththe nozzle 2 and the piping 3 being tubular members), in order to lowerthe fluid resistance within the pipeline R as much as possible, thinningprocessing is performed on the inner surfaces 4 on the joined end 2 aand 3 a sides of one or both of the tubular members 2 and 3 such thatthe inner surfaces 4 are formed mutually flush. Therefore, on thetubular members 2 and 3, a tapered surface 6 is formed on the innersurfaces 4 on the joined end 2 a and 3 a sides that have been thinningprocessed. Then, at the time of inspecting the welded portion M of bothsuch tubular members 2 and 3, the presence of defects in the flawinspection area S of the welded portion M is detected by deliveringultrasonic waves to the flaw inspection area S directly or by reflectionat the inner surfaces 4 (interfaces) of the tubular members 2 and 3,while scanning (moving) a probe 7 on the outer surfaces 5 of the tubularmembers 2 and 3.

However, conventionally, the tubular members of the nuclear power plant,such as the nozzle 2 of the nuclear reactor pressure vessel 1 and thepiping 3 that is butt welded to this nozzle 2, are not necessarilyformed (manufactured or designed) with consideration to the inspectionof the welded portion M by ultrasonic inspection following construction.Therefore there are cases where the length of the smooth section (linearportion) P1 of the outer surfaces 5 that extend in the axis O1 directionfrom the joined ends 2 a and 3 a of the tubular members 2 and 3 isshort, and the probe 7 cannot be scanned on the outer surfaces 5 of thetubular members 2 and 3 such that the entire flaw inspection area S iscovered. Furthermore, there are cases where the tapered surface 6 ispresent on a section near the joined ends 2 a and 3 a as a result ofthinning processing, so that the length of the smooth section (linearportion) P2 of the inner surfaces 4 that extend in the axis O1 directionfrom the joined ends 2 a and 3 a of the tubular members 2 and 3 isshort, and hence the path of the ultrasonic waves becomes complicateddue to reflections, making it difficult to ensure inspection accuracy,or the ultrasonic waves cannot be delivered to the entire flawinspection area S.

Means for Solving the Problem

The construction method of a pipeline of the present invention, is aconstruction method of a pipeline that forms a pipeline by joiningtubular members to each other by butt welding, and includes: a tubularmember preparation step for preparing a tubular member having a smoothlength of an outer surface along an axial direction from a joined end,which is set based on conditions of ultrasonic inspection of a weldedportion, which are determined by usage conditions of the pipeline; atubular member welding step for welding together prepared tubularmembers; and a welded portion inspection step for inspecting a weldedportion by ultrasonic inspection.

The tubular members of the present invention are tubular members thatare joined by butt welding to form a pipeline, and have a smooth lengthof an outer surface along an axial direction from a joined end, which isset based on conditions of ultrasonic inspection of a welded portion,which are deter mined by usage conditions of the pipeline.

The nuclear power plant of the present invention is furnished with thetubular member mentioned above as a nozzle.

In these aspects of the invention, for example, tubular members forwhich the smooth length of the outer surface is set based on conditionsfor ultrasonic inspection of the welded portion, which are determined bythe usage conditions of the class 1 or class 2 pipeline, which isclassified according to the importance of safety features of the nuclearpower plant, are prepared in the tubular member preparation step, andutilized in the construction.

That is to say, the tubular members are formed (designed) with thesmooth length of the outer surface set beforehand, so that at the timeof performing ultrasonic inspection of the welded portion by scanning aprobe transmitting ultrasonic waves on the outer surface of the tubularmember, for class 1, a flaw inspection area of the entire platethickness from the inner surface to the outer surface of the weldedportion can be inspected, and for class 2, a flaw inspection area of aplate thickness area of ⅓ of the designed plate thickness from the innersurface of the welded portion can be inspected.

Effects of the Invention

In the pipeline construction method, the tubular members, and thenuclear power plant of the present invention, the tubular members can bewelded to each other in the tubular member welding step, such that theconditions for the ultrasonic inspection of the welded portion, whichare determined by the usage conditions of the pipeline, can be satisfiedwith certainty. Furthermore, at the time of executing the ultrasonicinspection on the welded portion in the welded portion inspection step,since the smooth length of the outer surface (linear portion) of thetubular member is sufficiently ensured, the probe can be scanned on theouter surfaces of the tubular member such that the entire flawinspection area is covered, and areas in which flaws are not detectableare eliminated, and it becomes possible to perform inspection of thewelded portion certainly and favorably. Therefore, it becomes possibleto join the tubular members to each other by forming a welded portionwith a high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing tubular members (weldedportion) of a nuclear power plant according to an embodiment of thepresent invention.

FIG. 2 is a cross-sectional view showing tubular members (weldedportion) of a nuclear power plant according to an embodiment of thepresent invention.

FIG. 3 is a diagram showing a method for designing an outer surfacesmooth length of a tubular member of a nuclear power plant according toan embodiment of the present invention.

FIG. 4 is a diagram showing a method for designing an inner surfacesmooth length of a tubular member of a nuclear power plant according toan embodiment of the present invention.

FIG. 5 is a diagram showing a state in which ultrasonic inspection isbeing performed with an R-shaped probe.

FIG. 6 is a diagram showing a nuclear reactor pressure vessel (nuclearpower plant).

FIG. 7A and FIG. 7B are cross-sectional views both showing tubularmembers (welded portion) of a conventional nuclear power plant.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder, is a description of a pipeline construction method, tubularmembers, and a nuclear power plant, according to an embodiment of thepresent invention, with reference to FIG. 1 to FIG. 4, and FIG. 6. Here,in the present embodiment, the description is given assuming that thetubular members are tubular members that are joined by butt welding toform a pipeline R of a nuclear power plant 1.

With regard to the tubular members 10 and 11 that are joined by buttwelding in the present embodiment, as shown in FIG. 1 and FIG. 2,thinning processing is performed on the inner surfaces 4 on the joinedend 10 a and 11 a sides in order to reduce the fluid resistance withinthe pipeline R as much as possible, and the inner surfaces 4 of thetubular members 10 and 11 to be joined to each other are formed suchthat they become flush. As a result, by thinning processing the innersurfaces 4 on the joined end 10 a and 11 a sides, the tubular members 10and 11 can be formed such that they have a smooth section of the innersurface 4 which extends along the axis O1 direction from the joined ends10 a and 11 a, and a tapered surface 6 which connects between thissmooth section and the inside of the inner surface 4 which has not beenthinning processed.

Furthermore, in these tubular members 10 and 11, an inner surfacethinning angle θ1 of the tapered surface 6 is formed not exceeding afixed angle so that mode changes in the sound waves at the time of innersurface reflection are unlikely to occur.

Moreover, in the present embodiment, the tubular members 10 and 11 areformed (designed) such that; the length of the smooth section of theouter surfaces 5 that extend along the axis O1 direction from the joinedends 10 a and 11 a (outer surface smooth length, length of the linearportion), and the length of the smooth section of the inner surfaces 4that extend along the axis O1 direction from the joined ends 10 a and 11a (inner surface smooth length, length of the linear portion) arerespectively set based on the conditions of ultrasonic inspection of thewelded portion M, which are determined by the usage conditions of thepipeline R.

More specifically, in the present embodiment, the usage conditions ofthe pipeline R are set according to class 1 and class 2 (class 1equipment and class 2 equipment), in which the structures, the systems,and the equipment of the nuclear power plant 1 are classified accordingto the importance of their safety features. Class 1 represents theequipment (vessels, pipes, pumps, and valves) and the like thatconstitute the nuclear reactor coolant pressure boundary. The pair oftubular members 10 and 11 of this class 1 that are joined by buttwelding are for example the nozzle provided on the nuclear reactorpressure vessel 1 and the pipeline that is joined to this nozzle.Furthermore, class 2 represents the equipment (vessels, pipes, pumps,valves) and the like for which the importance of the safety features islower than class 1.

Moreover, in the present embodiment, the conditions for ultrasonicinspection of the welded portion M, which are determined by the usageconditions of such a pipeline R, are the areas of inspection prescribedby the “Standards for Nuclear Power Plants: Maintenance Standards”mentioned above. That is to say, under the conditions of class 1, asshown in FIG. 1, the entire plate thickness t from the inner surface 4to the outer surface 5 of the welded portion M is made the flawinspection area S, and under the conditions of class 2, as shown in FIG.2, a plate thickness area of ⅓ of the designed plate thickness t fromthe inner surface 4 of the welded portion M is made the flaw inspectionarea S.

Then, based on such conditions for ultrasonic inspection of the weldedportion M, at the time of setting the smooth length of the outer surface5 (in the design method for the smooth length of the outer surface 5),as shown in FIG. 3, selection between class 1 and class 2 is performed,and in the selected class, selection is made of an inspection menu to beutilized in the design.

At this time, in a case where class 1 is selected, an inspection menu isselected so that in the ultrasonic inspection, 2 tan θ at the time of a1-skip flaw detection, and tan θ at the time of a 0.5-skip flawdetection, become a maximum. On the other hand, in a case where class 2is selected, an inspection menu is selected so that in the ultrasonicinspection, (4/3) tan θ at the time of a 1-skip flaw detection, and tanθ at the time of a 0.5-skip flaw detection, become a maximum.

Here, θ represents the ultrasonic wave incidence angle. Furthermore,1-skip in ultrasonic inspection means that the ultrasonic waves aredelivered to the flaw inspection area S (welded portion M) of theinspected site by entering from the outer surface 5 (end face) of thetubular members 10 and 11 and being reflected once at the inner surface4, and 0.5-skip means that the ultrasonic waves are delivered directlyto the flaw inspection area S (welded portion M) of the inspected site,by entering from the outer surface 5 of the tubular members 10 and 11.

Next, the skip selection is performed. In a case where class 1 isselected and 1-skip is selected, the outer surface smooth length L1 (mm)is calculated by formula (1), and in a case where class 1 is selectedand 0.5-skip is selected, the outer surface smooth length L2 (mm) iscalculated by formula (2). Furthermore, in a case where class 2 isselected and 1-skip is selected, the outer surface smooth length L3 (mm)is calculated by formula (3), and in a case where class 2 is selectedand 0.5-skip is selected, the outer surface smooth length L4 (mm) iscalculated by formula (4). Here t (mm) represents the thickness (designplate thickness) of the tubular member.

L1=(2×t×tan θ)+(probe play)+(probe individual difference)+(scanningallowance)  (1)

L2=(t×tan θ)+(probe play)+(probe individual difference)+(scanningallowance)  (2)

L3=((4/3)×t×tan θ)+(probe play)+(probe individual difference)+(scanningallowance)  (3)

L4=(t×tan θ)+(probe play)+(probe individual difference)+(scanningallowance)  (4)

By so doing, it is possible to provide a method that prescribes theouter surface smooth lengths L1 to L4 with respect to a variety ofcombinations of the plate thickness t and the ultrasonic wave incidenceangle θ.

Furthermore, at this time, it is desirable to use the axial length H ofthe probe 7 in the calculation of the (probe play), the (probeindividual difference), and the (scanning allowance). For example, theprobe axial length is made H (mm), and the (probe play)=H/2, the (probeindividual difference)=H/2, and the (scanning allowance)=H/2. As aresult, it is possible to provide a simple and valid prescription methodfor the (probe play), the (probe individual difference), and the(scanning allowance).

On the other hand, at the time of setting the inner surface smoothlength (length of the inner surface thinning) based on the conditions ofthe ultrasonic inspection of the welded portion mentioned above (designmethod for the inner surface smooth length), then as shown in FIG. 4,class 1 or class 2 is selected, and the inspection menu in the selectedclass utilized in the design is selected.

At this time, irrespective of whether class 1 or class 2 is selected, aslong as there is a 1-skip in the inspection menu, the inspection menu inwhich the ultrasonic wave incidence angle θ becomes a maximum isselected.

Next, the skip selection is performed. In a case where class 1 isselected and 1-skip is selected, the inner surface smooth length L5 (mm)is calculated by formula (5), and in a case where class 1 is selectedand 0.5-skip is selected, the inner surface smooth length L6 (mm) iscalculated by formula (6). Furthermore, in a case where class 2 isselected and 1-skip is selected, the inner surface smooth length L7 (mm)is calculated by formula (7), and in a case where class 2 is selectedand 0.5-skip is selected, the inner surface smooth length L8 (mm) iscalculated by formula (8).

L5=(t×tan θ)+(flaw inspection area/2)+(ultrasonic wave spreadwidth)  (5)

L6=(flaw inspection area/2)+(ultrasonic wave spread width)  (6)

L7=((1/3)×t×tan θ)+(flaw inspection area/2)+(ultrasonic wave spreadwidth)  (7)

L8=(flaw inspection area/2)+(ultrasonic wave spread width)  (8)

As a result, it is possible to provide a method that prescribes theinner surface smooth lengths L5 to L8 with respect to a variety ofcombinations of the plate thickness t and the ultrasonic wave incidenceangle θ.

Furthermore, at this time, it is desirable to make the ultrasonic wavespread width the size of the oscillator of the probe 7.

By so doing, it is possible to provide a valid and a simple index valuefor the ultrasonic wave spread width.

In the present embodiment, as described above, the tubular members 10and 11 for which the outer surface smooth lengths L1 to L4 and the innersurface smooth lengths L5 to L8 have been set based on the conditions ofthe ultrasonic inspection of the welded portion M, which is determinedaccording to the usage conditions of the pipeline R, are prepared in thetubular member preparation step, the prepared tubular members 10 and 11are welded to each other in the tubular member welding step, and thewelded portion M is inspected by executing the ultrasonic inspection inthe welded portion inspection step.

At this time, the tubular members 10 and 11 are formed (designed) withthe outer surface smooth lengths L1 to L4, the inner surface smoothlengths L5 to L8, and the inner surface thinning angle θ1 setbeforehand, so that when the ultrasonic inspection of the welded portionM is performed by scanning the probe 7 transmitting ultrasonic waves onthe outer surfaces 5 of the tubular members 10 and 11, for class 1, asshown in FIG. 1, a flaw inspection area S of the entire plate thicknesst from the inner surface 4 to the outer surface 5 of the welded portionM can be inspected, and for class 2, as shown in FIG. 2, a flawinspection area S of a plate thickness area of ⅓ of the designed platethickness t from the inner surface 4 of the welded portion M can beinspected.

As a result, in the pipeline R construction method, the tubular members10 and 11, and the nuclear power plant of the present embodiment, thetubular members 10 and 11 can be welded to each other in the tubularmember welding step, such that the conditions for the ultrasonicinspection of the welded portion M, which are determined by the usageconditions of the pipeline R, can be satisfied with certainty.

Furthermore, at the time of executing the ultrasonic inspection on thewelded portion M in the welded portion inspection step, since the outersurface smooth lengths L1 to L4 of the tubular members 10 and 11 aresufficiently ensured, the probe 7 can be scanned on the outer surfaces 5of the tubular members 10 and 11 such that the entire flaw inspectionarea S is covered, and areas in which flaws are not detectable areeliminated, and it becomes possible to perform inspection of the weldedportion M certainly and favorably.

Moreover, at the time of executing the ultrasonic inspection on thewelded portion M, in addition to the outer surface smooth lengths L1 toL4 of the tubular members 10 and 11, the inner surface smooth lengths L5to L8 are also sufficiently ensured. Furthermore, the inner surfacethinning angle θ1 is formed not exceeding a fixed angle so that modechanges in the sound waves at the time of inner surface reflection areunlikely to occur. As a result, there is no longer the situation wherethe path of the ultrasonic waves becomes complicated due to reflections,or the ultrasonic waves cannot be delivered to the entire flawinspection area S.

Therefore, according to the pipeline R construction method, the tubularmembers 10 and 11, and the nuclear power plant of the presentembodiment, it becomes possible to join the tubular members 10 and 11 toeach other by forming a welded portion M with a high reliability.

The foregoing has described an embodiment of the pipeline constructionmethod, the tubular members, and the nuclear power plant according tothe present invention. However the present invention is in no waylimited to the embodiment mentioned above, and appropriate changes arepossible within a scope that does not depart from the gist thereof.

For example, as shown in FIG. 5, an R-shaped probe furnished with acurved surface may be used, and the (probe play) at the time of thecalculation of the outer surface smooth lengths L1 to L4 may be madesmaller than H/2. In this case, it becomes possible to achieve areduction in the necessary outer surface smooth lengths L1 to L4.

Furthermore, in the case of a subject where the inspection is performedby combining a plurality of methods with different ultrasonic waveincidence angles θi and skips, a combination of the following formulas(9) to (12) that gives the largest value may be utilized in designingthe outer surface smooth lengths L1 to L4. Here, in the case of class 1,formula (9) represents a 1-skip inspection and formula (10) represents a0.5-skip inspection. Furthermore, in the case of class 2, formula (11)represents a 1-skip inspection and formula (12) represents a 0.5-skipinspection. In such a manner, even in a case where a plurality ofmethods is combined, it becomes possible to simply determine theconditions that become the most constraining.

2×tan θi  (9)

1×tan θi  (10)

4/3×tan θi  (11)

1. A construction method of a pipeline that forms a pipeline by joiningtubular members to each other by butt welding, comprising: a tubularmember preparation step for preparing a tubular member having a smoothlength of an outer surface along an axial direction from a joined end,which is set based on conditions of ultrasonic inspection of a weldedportion, which are determined by usage conditions of said pipeline; atubular member welding step for welding together prepared tubularmembers; and a welded portion inspection step for inspecting a weldedportion by ultrasonic inspection.
 2. A construction method of a pipelineaccording to claim 1, wherein, in said tubular member preparation stepthere is provided a tubular member having said outer surface smoothlength, and an inner surface smooth length along an axial direction froma joined end, which is set based on conditions of ultrasonic inspectionof a welded portion, which are determined by usage conditions of saidpipeline.
 3. A construction method of a pipeline according to claim 1,wherein a probe used in said ultrasonic inspection is an R-shaped probefurnished with a curved surface.
 4. A construction method of a pipelineaccording to claim 2, wherein a probe used in said ultrasonic inspectionis an R-shaped probe furnished with a curved surface.
 5. Tubular membersthat are joined by butt welding to form a pipeline, and have a smoothlength of an outer surface along an axial direction from a joined end,which is set based on conditions of ultrasonic inspection of a weldedportion, which are determined by usage conditions of said pipeline. 6.Tubular members according to claim 5, that have said outer surfacesmooth length, and an inner surface smooth length along an axialdirection from a joined end, which is set based on conditions ofultrasonic inspection of a welded portion, which are determined by usageconditions of said pipeline.
 7. A nuclear power plant furnished with atubular member according to claim 5 as a nozzle.
 8. A nuclear powerplant furnished with a tubular member according to claim 6 as a nozzle.